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The effects of length of cut and mechanical processing on corn silage utilization by dairy cows were evaluated. Corn silage treatments were harvested at the black line stage of maturity and chopped at a theoretical length (TLC) of 9.5 mm without processing (Control) or at a TLC of 19 mm with processing at roller clearances of 1, 3, or 5 mm. Eight multiparous Holstein cows were assigned in a replicated 4 x 4 Latin square design with 21-day periods. Corn silage treatments were fed in diets containing 78.3% corn silage and 21.7% soybean meal (DM basis). Treatments had no significant effects on DMI, milk and 4% FCM production. The efficiency of converting DMI to FCM tended to be greater with processing at a roller clearance of 1 and 3 mm than at other clearances. Apparent total tract digestibility of starch tended to be lowest for cows fed control silage, and increased as roller clearance decreased. Ruminal ammonia concentrations in cows fed control silage were numerically higher than in cows fed proccesed silages. These results suggest that when corn silage is harvested at the black line of maturity, roller clearance should be 3 mm or less with a TLC of 19 mm.

. Effect of mechanical processing of corn silage on in vitro ruminal fermentation, and in situ bacterial colonization and dry matter degradation. Can. J. Anim. Sci. 87: 259-267. Rumen fermentation and bacterial colonization of mechanically processed corn silage were evaluated in a series of in vitro and in situ experiments using ruminally cannulated cows. Data from rumen-simulated continuous culture (Rusitec) showed that total VFA concentration was increased (P < 0.001) by feeding processed corn silage, while pH was reduced (P < 0.001) and ammonia nitrogen remained unchanged (P > 0.05). Mechanical processing enhanced the in situ rate and extent of dry matter disappearance for corn stems and kernels, respectively (P < 0.05). It also enhanced in situ, the initial attachment of rumen bacteria responsible for corn digestion, as monitored by real-time PCR. The16S rDNA copy numbers of amylolytic and lipolytic bacteria, such as Succinivibrio dextrinosolvens, Ruminobacter amylophilus and Anaerovibrio lipolytica, attached to corn kernels were increased for processed corn silage (P < 0.05), in particular at 2 h after the start of incubation. In addition, corn stemattached cellulolytic and hemicellulolytic bacteria, such as Fibrobacter succinogenes, ruminococci and Eubacterium ruminantium, increased in 16S rDNA copy numbers for processed corn silage (P < 0.05). This was observed for the initial incubation period from 10 min to 2 h. These results demonstrate more rapid attachment and heavier colonization of rumen bacteria to the processed compared with the unprocessed silage, which facilitates ruminal digestion and fermentation.Key words: Corn silage, mechanical processing, rumen fermentation, bacteria, attachment Kozakai, K., Nakamura, T., Kobayashi, Y., Tanigawa, T., Osaka, I., Kawamoto, S. et Hara, S. 2007. Incidence du conditionnement mécanique sur la fermentation in vitro de l'ensilage de maïs dans le rumen ainsi que sur sa colonisation par les bactéries et la dégradation de la matière sèche in situ. Can. J. Anim. Sci. 87: 259-267. Les auteurs ont étudié la fermentation de l'ensilage de maïs conditionné mécaniquement et sa colonisation par les bactéries du rumen dans le cadre d'une série d'expéri-ences in situ et in vitro en recourant à des vaches canulées au rumen. Les données issues des cultures continues simulant le rumen (Rusitec) montrent que le conditionnement de l'ensilage augmente la concentration totale d'acides gras volatils (P < 0,001) tout en réduisant le pH (P < 0,001), sans modification de la concentration d'azote ammoniacal (P > 0,05). Le conditionnement mécanique accroît le taux de disparition in situ de la matière sèche et la quantité totale de matière sèche dégradée, respectivement pour les rafles et les grains de maïs (P < 0,05). In situ, il améliore aussi la fixation initiale des bactéries du rumen responsables de la digestion du maïs, telle que suivie par PCR en temps réel. On note une hausse du nombre de copies de l'ADNr 16S des bactéries amylolytiques et lipolytiques comme Succinivibrio dextrinos...

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The experiment was conducted to evaluate the effect of roll clearance of mechanical processing of whole plant corn silage (CS) on carbohydrate and protein utilization in dairy cows. Treated CS was harvested at the black-line stage of maturity and chopped at a theoretical length of cut (TLC) of 9.5 mm without processing or at a TLC of 19 mm with processing at a roll clearance of 1, 3 and 5 mm. Four ruminally and duodenally cannulated dry cows were assigned to a 4 × 4 Latin square design for 14-day periods. Cows were fed diets containing 77% CS and 23% soybean meal (dry matter basis) to equalize the crude protein supply. Mechanical processing had no significant effect on dry matter intake and neutral detergent fiber digestibility. Ruminal and total tract starch digestibility and total digestible nutrients tended to be higher with processing at a roll clearance of 1 or 3 mm than at 5 mm. Microbial nitrogen efficiency in cows did not differ among all treatment groups. These results suggest that when CS is harvested at the black-line stage of maturity, roll clearance should be 3 mm or less with a TLC of 19 mm.